1. Field of the Invention
The invention relates to a compressor blow-off or discharge arrangement; more specifically the invention relates to means for supporting and guiding a ring serving as a valve member controlling a compressor blow-off or discharge opening.
2. Summary of the Prior Art
In a gas turbine engine it is known to combine with the compressor blow-off valves arranged in association with one or more stages, intended to deflect part of the air flow outwards when the compressor is made to operate outside the range for which it was designed, under a partial load, for example. In this way the so-called "surging" phenomenon, due to the air flows breaking away from the blades and resultant instability of flow, is avoided.
Conventional blow-off means comprise several pivotal flaps distributed over the periphery of the casing defining the flow path and these flaps are synchronously controlled. The flaps should present a substantial flow section, be able to open and close quickly, and provide good seals in the closed position so as to avoid adverse effects on the performance of the engine. To meet these requirements heavy, complex arrangements, of far from negligible overall size are necessary. Moreover, the opening of these flaps creates in the air flow turbulence and other phenomena such as heterogeneity which may disturb the operation of any downstream compressor.
One prior proposal consists in making axial movement arrangements comprising a ring-shaped valve surrounding the casing defining the air flow path, and the axial motion of which, which may be combined with rotation, uncovers a slot or other opening in the periphery of the flow path. By this means it is possible to control a substantial flow of air over the relatively short range of movement of the ring, the overall size of which is small; finally, a better distribution of the stresses together with a simpler construction is achieved.
Such a ring or other annular assembly, having a substantial diameter, is actuated by a plurality of actuators distributed over its periphery. Usually, it is supported and guided for movement by means of slides or rollers cooperating with other sliding or rolling surfaces. U.S. Pat. No. 588,268, for example, discloses a guide arrangement in which slides, evenly distributed over the radially inner face of the ring, are mounted to slide on longitudinal ribs added on the outer wall of the casing. Patent DE-A-2 060 509 also shows guide means in which rails rigid with the ring cooperate with rollers mounted on the casing.
Such means are not satisfactory as they are subject to wear and to jamming owing to clogging up as a result of particles which insert themselves between the relatively sliding surfaces. The inevitable deformations at diameters of this order also bring about jamming which effectively locks the mechanism. Finally, the ring is not adequately supported with the necessary degree of rigidity because of the play necessary for satisfactory operation, which permits the development of vibrations.
An object of the invention is to overcome the disadvantages of prior proposals.